1. Field of the Invention
The present invention relates generally to methods and apparatus for forming parts by the successive stacking of a number of laminas, and more particularly to such methods and apparatus for maintaining the vertical truness of the stack of such laminas.
2. Description of the Prior Art
It is well known that certain structures may be formed by the stacking of a series of laminations or laminas. For example, elements of electric motors, solenoids and transformers may be formed by this process. Typically, the laminas are blanked from continuous strip stock and then stacked and bound together to form the part being manufactured. However, due to imperfections of the strip stock, thickness variations of the strip stock often occur and may thus cause the part being formed from successive layers of the laminas to incur parallelism error (i.e., "leaning"). This parallelism error occurs because in stacking the laminas, the relatively thicker portions of the laminas are directly overlaying one another, and the relatively thinner portions of the laminas directly overlie one another. Parallelism error is depicted in prior art FIG. 1. During the stacking of the individual laminations 10, one side 12 of the stack becomes higher than the opposite side 14 of the stack, which in turn results in a leaning or bending of the stack.
Techniques have been developed in the industry for attempting to overcome this leaning condition of the stack. For example, it is known in the industry to rotate the stack for symmetrical laminas so that the relatively thicker portion of each lamina does not directly overlie or underlie the relatively thicker portion of adjacent laminas. Typically the stack is rotated 180.degree. prior to the laying of each lamina. Of course, instead of rotating the stack, each lamina may be rotated while the position of the stack is kept constant to achieve the same result. U.S. Pat. No. 4,619,028 to Neuenschwander describes this solution to the problem associated with parallelism error.
Rotating the laminas in order to reduce the effects of parallelism error may be performed if the laminas are symmetrical. However, this rotational technique cannot be used for laminations that are not symmetrical to overcome the effects of transverse thickness variations in the laminas.
It is also generally known in the industry to provide laminas with depressions, known in the industry as "dimples". Heretofore, dimples have been provided on laminas in order to provide separation between adjacent laminas when the stacked laminas are to be annealed. Separation of the laminas during the annealing process of the stack is advantageous because it allows for the surfaces of the laminas to be in fluid communication with the ambient atmosphere during the annealing process. Heretofore, dimples have been provided upon the laminas such as by using alternating dies in which both the dies locate the dimples on alternating sides of the lamina so that the dimples do not overlie one another as described in U.S. Pat. No. 4,538,345 to Diederichs. In addition to using alternating dies, dimples have also been provided upon alternating sides of the laminas by rotating the laminas as described in U.S. Pat. No. 5,349,741 to Neuenschwander.
Methods and apparatus are needed to effectively overcome the effects of parallelism error during the fabrication of structures by the stacking of laminations. Such methods and apparatus should not require the rotation of individual laminas or of the lamina stack and which may therefore be utilized in connection with symmetrical as well as nonsymmetrical laminas.